Another ISO 8601:1998 Brainstorm

While I am waiting to receive the 1996 ISO 8601 revision proposal,
here one further idea: allow a 0 value to mean "not known" in all the
date notations, i.e. in a fixed width format, 1997-07 could also
be stored as 1997-07-00. I have seen this technique used in at least
one database so far (DIN's PERINORM).
A silly question from a non-native English speaker: what is the difference
between "not known" and "not specified"? There are codes for both
situations defined in ISO 5218 and I never understood, why. See <ftp://ftp.informatik.uni-erlangen.de/pub/doc/ISO/ISO-5218-summary>
for the full text of this standard.
What about 1492J-09-31 refering to a date in the Julian calendar
and B0345J-02-13 refering to February 2, 345 B.C.E. in the Julian
calendar? I guess, no matter what we do with negative years,
lexical sorting and comparing will always be messed up.
Markus
--
Markus G. Kuhn, Computer Science grad student, Purdue
University, Indiana, USA -- email: kuhn at cs.purdue.edu